In a conventional copying machine in which copying magnification can be changed, and of such a type that keys are provided for each of the predetermined copying magnifications, there must be provided a number of key switches with a complicated circuit arrangement, thereby causing an increase in the production cost of the copying machine. Another type of machine exists, wherein only one key is provided so that the copying magnification can be changed from one magnification ratio to another magnification ratio step by step each time said key is operated, and the desired magnification ratio can be set by ceasing the operation of the key. Upon operation of the key by a predetermined number of times, the magnification ratio can return to an original value. In this type or machine, the key must be operated a number of times, the operation of the key is troublesome. Another disadvantage of the conventional copying machine is that in a case where the original to be copied has an irregular paper size, the most suitable magnification ratio can not be designated. Even if the copying magnification ratio can be set as a desired value for the irregular size original, it is necessary to memorize the magnification ratio which is once set, and updating the past memorized magnification ratio, whereby the magnification ratio set previously are not available once a new magnification ratio is set in the copying machine.